Mobile data is growing at an astounding rate, both in terms of mobile subscribers as well as mobile data traffic. The exponential growth of mobile data requires substantial increase of network capacity and network efficiency. Currently, the existing third generation (3G) mobile network faces network congestion problem, resulting in failed calls, lower data rates and slow response times, in numerous markets. Concurrent with the data traffic growth, the rapid uptake of Smartphone subscribers, such as iPhone, Android phone and Blackberry phone users, have put additional pressure on the mobile network, due to the support of true always-on features. The always-on feature creates several problems. First, many of the always-on features generate frequent traffic, such as keep alive and status update. Second, it significantly increases signaling in the network, due to frequent context establishment and release. Third, it negatively affects user devices' battery life. Fourth, the overhead to support the always-on feature is very large compare to its data payload.
Long Term Evolution (LTE) is an improved universal mobile telecommunication system (UMTS) that provides higher data rate, lower latency and improved system capacity. In the LTE system, an evolved universal terrestrial radio access network includes a plurality of base stations, referred as evolved Node-Bs (eNBs), communicating with a plurality of mobile stations, referred as user equipment (UE). A UE may communicate with a base station or an eNB via the downlink and uplink. The downlink (DL) refers to the communication from the base station to the UE. The uplink (UL) refers to the communication from the UE to the base station. The LTE system is better adapted from the beginning to handle always-on traffic. For example, the LTE system supports longer sleep modes in connected mode, dynamic capacity in physical layer control channel and flexibility in extending core network signaling capacity by Mobility Management Entity (MME).
Despite the improvements in the LTE system, it still faces capacity and efficiency problems. For example, mobile network operators always prioritize real-time voice traffic over data traffic. Resources are held in reserve across the network for circuit-switched voice traffic. New wireless data network, such as 3G and LTE network, also optimizes support for large amount of data traffic, such as video conferencing. Such design, however, does not work well for applications with short, infrequent data sessions, such as chatty applications and keep alive messages. Many common applications such as news, weather, and social networking, periodically connect and disconnect to/from the network for updates. These applications contain small amount of user data while still require a large amount of signaling traffic to establish and tear down the session. It is estimated that with the growing number of Smartphone applications over the network, the signaling overhead outpaces the data traffic by 30% to 50%, if not higher. These applications create large control overhead and signaling load. UE battery life also becomes a major concern, because the frequent background traffic is not optimized for battery consumption. Further, although UE long sleep cycles help to increase UE battery life, it does not work very well for network-controlled handover. When the UE is in long sleep cycle, it does not perform mobility measurements. The network ends up with less accurate measurement to make assistance efficiently in preparing handover for the UE.
The first issue relates to discontinuous reception (DRX) or discontinuous transmission (DTX) transitions. In 2G and 3G, the UE uses discontinuous reception (DRX) in idle state to increase battery life. The LTE system has introduced DRX in the connected state. Long DRX in the connected state helps to improve battery life and reduces network signaling overhead. However, the connected state DRX in current LTE does not give any traffic shaping benefits in the uplink. Although traffic shaping is available for downlink in connected state DRX, it is defined rigidly. The traffic shaping does not consider any information about traffic type or UE state. Such design limits the benefit of the connected mode dormancy feature.
The second issue relates to UE going into idle mode transition. Similar network inefficiency problems in the LTE system are related to transitioning into idle state. There are two radio resource control (RRC) states, namely, RRC IDLE state and RRC CONNECTED state. Currently, the transition from the RRC CONNECTED state to RRC IDLE state is controlled by the network. The main purpose to transition into RRC IDLE state is for power saving. However, the RRC state transition incurs large signaling overhead. Further frequent RRC state changes may also impose significant more use of system resource, resulting in increased signaling overhead in the network. For some application traffic, the current RRC state transition design may counteract the power saving and/or system efficiency.
The third issue relates to UE measurement report and radio link failure (RLF) detection. One problem in the current LTE system is that the UE measurement and measurement report triggering are rigid. They are not adapted to the UE traffic types, such as background traffic, power-saving or non-power-saving state. Further, the UE considers RLF to be detected upon physical layer problems based on a procedure of N310/N311/T310, random access problem indication from MAC layer, and indication from radio link control (RLC) layer that the maximum number of retransmission has been reached. Once RLF is detected, the UE gathers and stores RLF information and attempts RRC connection reestablishment. If such attempt fails, the UE goes back to RRC IDLE state. Therefore, once UE considers RLF is detected, it will invoke a series of costly procedures. The current RLF triggering does not consider the traffic type, such as background traffic, power-saving or non-power-saving state. This could result in prematurely declaring RLF and trigger non-access stratum (NAS) recovery that follows a failed RRC re-establishment, which generates additional core network signaling.
Solutions are sought.